Updated TODO list.
Added a stub PNAS template to the templaes/ folder.
Added example7 to docs.
Adjusted the order of code blocks inside format_bibitem().

This allows the user-defined variables to occur earlier on in the chain of events inside format_bibitem(), so that a user-defined variable can be used to modify the citelabel. Before, the user-defined variables were defined after the citation label was already written out to the BBL file.